Variable resistance



B. D. LEE

VARIABLE RESISTANCE June 20, 1950 2 Sheets-Sheet 1 Filed March 29, 1948 FIG.

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VARIABLE maszs'rmcs 2 Sheets Sheet 2 Filed March 29, 1948 A A w A 2 A m dmmm INVENTOR. BURTON 0. LEE

ATTORNEY Patented June 20, 1950 VARIABLE RESISTANCE Burton D. Lee, Houston, Tex., assignor to The Texas Company, New York, N. Y., a corporation of Delaware Application March 29, 1948, Serial No. 17,753

6 Claims.

This invention is concerned with variable resistances, including potentiometers, and provides improved apparatus of such type. The apparatus of the invention requires but few resistance elements or units in proportion to the number of possible settings and it can be set at any desired decimal value accurately and conveniently.

In its preferred form the apparatus of the invention contemplates a push-button type potentiometer employing only four-ninths of the resistance elements customarily employed in such apparatus and permitting variations in voltage while maintaining constant load on the input line. The apparatus of the invention is generally useful in laboratory work and the like in which it is frequently desirable to set voltage or resistance accurately and rapidly according to the decimal system. However, it has particular utility in electrical computers and in electrical analogue apparatus such as the potentiometric models disclosed and claimed in co-pending application Serial No. 791,796, filed December 15, 1947, by Alexander Wolf and myself.

In essence, the apparatus of the invention comprises four resistance elements respectively of one, two, three, and six unit values, together with a plurality of double pole single throw switches. preferably arranged side by side in a decade box and connected in a circuit with the resistance elements in such fashion that throwing in one switch puts one unit of resistance into the circuit, throwing in a second switch throws in two units of resistance, etc., until the throwing in of the ninth switch throws in nine units of resistance. If desired, the throwing in of a tenth switch will close the circuit without throwing in any of the resistance elements. Means should be provided for opening all of the switches save one automatical- 1y when that one is closed or thrown, so that by closing a single switch, preferably of the pushbutton type, its corresponding resistance (which may be any value from zero to nine units) is automatically connected across the circuit.

In accordance with the invention, a number of the decade switch-resistance combinations described above may be connected in series. The first series for example, may have resistances of one, two, three, and six ohms, with the second resistance series of ten, twenty, thirty, and sixty ohms and the third series of one hundred, two hundred, three hundred, and six hundred ohms. In this fashion, any resistance value from zero to 999 ohms may be connected in the circuit by pushing three buttons, one in each of the three decade Switches.

I prefer to construct the apparatus employing four-pole single-throw switches, with two sets of four resistances each connected to each decade switch block, the arrangement being such that the resistance across the input of the potentiometer is maintained constant, as described in detail hereinafter.

These and other aspects of my invention will be apparent in the light of the following detailed description taken in conjunction with the accompanying drawings in which:

Fig. 1 is a plan view of a push-button type potentiometer constructed in accordance with my invention and provided with three banks of ten switches each;

Fig. 2 is a longitudinal elevation, partly in section, through one bank of switches of Fig. 1;

Fig. 3 is a diagram showing one of the switches of Fig. 1 in cross section connected to a group of resistances;

Fig. 4 is a schematic diagram illustrating the over-all action of the potentiometer of Figs. 1, 2 and 3; and

Fig. 5 is a detailed wiring diagram of this potentiometer.

Fig. 1 shows the front of a panel l0 upon which are mounted three banks I I, l2, l3 of push-button switches, ten to a bank and numbered from 0 to 9. Each bank of switches is so constructed that when any one switch is pushed into closed position any previously closed switch or switches in that bank are opened. The left hand bank ll of switches represents resistance values of 1000 to 9000 ohms; the middle bank l2 represents resistances of 100 to 900 ohms and the right hand bank represents resistances of 10 to ohms. The buttons are numbered to correspond to the resistances they control, so that by pushing button No. 3 in the left bank, button No. '7 in the middle bank and button No. 8 in the right bank, a total resistance of 3780 ohms is connected across a circuit.

The mechanical relationship of the switches of any bank is shown in Fig. 2. Each switch 14 of the bank has a push-button or key l5 mounted on top of a bar [6 which moves up and down, as shown in Fig. 2. The bar has a latch ll on one side which works against a gang bar 18 extending along all the switches and having limited horizontal movement permitted by a leaf spring IRA at the end of the bank. When any switch button is depressed, the gang bar is moved slightly to the right, releasing any switches which have been depressed previously. Each switch bar is provided with a compression spring 19 which forces it up and opens the switch when the gang bar releases the latch on the bar, so that only the switch last pushed down is caught and held by the gang bar, which rides in above the latch of that bar under the force of the leaf spring. This is only one of a number of conventional ganged switch mechanisms which may be employed in the structure of the invention, since there are various combinations which assure the release and opening of all switches in a decade system, save the one which is pushed or closed.

Fig. 4 is a schematic diagram illustrating the over-all arrangement of the potentiometer of Figs. 1 to 5. The voltage input to the instrument is imposed from line A to line B, and the output is across line A and line C, the potentiometer 20 being shown as composed of two equal slide wire resistances 2i, 22 (which are parallel to each other mechanically) and a double slider 23 which is connected to line C, the resistance 2| being connected to line B and the other resistance 22 being connected to line A. In other words, the circuit is such that, irrespective of the potentiometer setting, the resistance between lines A and B is constant, since the contribution of one resistance element decreases as that of the other element increases. However, as the slider is moved down in Fig. 4 the resistance between lines A and C decreases while the resistance between lines B and C increases by a like amount. In consequence the input load on the potentiometer (from line A to line B) remains constant for any potentiometer setting, which is important in many types of potentiometric operations.

The results obtained with a slide wire potentiometer such as that exemplified in Fig. 4 are obtained in the preferred form of the apparatus of the invention without any of the difficulties encountered with slide wires in settin a particular value. For example, if a resistance of 1230 ohms is required, No. 1 switch in the left hand bank,

No. 2 switch in the middle bank and No. 3 switch in the right hand bank are closed, whereupon the circuit resistance from line A to line C (see Fig. 5) will be 1230 ohms, while the resistance from line C to line B will be 8760 ohms, and the resistance from line A to line B will be the sum of these resistances or 9990 ohms.

Each switch bank comprises ten double pole single throw switches and operates in combination with two sets of resistances. Thus, as shown in Fig. 5, the left hand bank has one set composed of four resistances respectively of 1000, 2000, 3000, and 6000 ohms and another set of 6000, 3000, 2000, and 1000 ohms respectively. The middle bank likewise has two sets of resistances of just onetenth the value of corresponding resistances of the left bank, and the right bank has two sets of resistances having one-hundredth of the values of those in the left bank.

The right hand sets of resistances of the three banks correspond to the resistance 2| in Fig. 4, and the left hand sets of resistances of the three banks correspond to the resistance 22 of Fig. 4, and the several sets are connected in a circuit with the switches and with the lines A, B and C so that by punching one button in each of the three banks any value of resistance from to 9990 ohms in increments of ten can be imposed between line A and line C while a value equal tc 9990 minus the resistance between A and C is imposed between lines B and C.

As shown in Fig. 3 (and also diagrammatically as switch No. 2 of the left hand bank of Fig.

each switch I has 4 poles 24, 25, 26, 21 and eight tacts and the poles are connected into the resistance circuits of each bank.

To consider the resistances connected across BC of Fig. 5, it will be observed that starting on the right at line B the current flow is through No. 1 of the left hand bank to its right hand 6000 ohm resistance in series with its right hand 2000 ohm resistance and thence to line C. The total resistance in ohms across BC is thus 60+600+100+6000+2000=8760.

The resistances connected between lines A and C for this switch setting may be traced similarly. Beginning at the right on line A the current flow is through switch No. 3 of the right hand bank to its left hand 30 ohm resistance, thence through switch No. 2 of the middle bank to its left hand 200 ohm resistance and thence through switch No. 1 of the left hand bank to its left hand 1000 ohm resistance and thence to line C. The total resistance A to C is thus 30+200+1000=l230 ohms.

The circuit arrangements of the three banks are the same and other possible settings of the potentiometer will be plain from a consideration of any of them. If switch No. 9 of the middle bank is closed, 600 ohms in series with 300 ohms will be connected across AC and BC will be short circuited, i. e. without resistance as far as the middle bank is concerned. If switch No. 3 of the middle bank is closed, 600 ohms in series with 200 ohms will be connected across AC and 100 ohms will be connected across BC.

Other possible settings of the middle bank are as follows:

Resistance Resistance Switch No. (ohms) (ohm A to C B to C The values appearing in the right hand column under Resistance (ohms) B to C pertain to the resistance value inserted in the circuit by the middle bank only.

From the foregoing it will be apparent that with four resistances any value from zero through decades to may be connected A to C while any value from 90 in decades to zero may be connected B to C. In other words, four resistances in each side of the circuit serve the purpose of nine.

Of course, when it is unnecessary to maintain a constant resistance across the input, double pole instead of four pole switches may be employed, i. e. the resistances and switch poles on one side of all banks may be eliminated.

If desired, additional switch bank-resistance combinations may be added to either end of the circuit of Fig. 5. For example, a bank identical to the left hand bank, save for the use of 10,000 ohm, 20,000 ohm, 30,000 ohm and 60,000 ohm resistances can be added to the left of the circuit of Fig. 5 in which case by punching four buttons,

any value (in multiples of ten) from 99,990 ohms to zero could be set A to C, with to 99,990 ohms (in multiples of ten) set 8 to C, the resistance A to B being constant.

The apparatus of the invention is compact, economical to build, and convenient to use. Its settings are positive and accurate and can be duplicated repeatedly without the dimculties encountered in settings of slide-wire type variable resistances and potentiometers.

I claim:

1. In a variable resistance, the combination which comprises four resistances, having respective values of one, two, three and six units, a circuit, at least nine switches, one connecting the one unit resistance in the circuit upon closing, a second connecting the two unit resistance in the circuit upon closing, a third connecting the three unit resistance in the circuit upon closing, a fourth connecting the three and one unit resistances in series in the circuit upon closing, a fifth connecting the three and two unit resistances in series in the circuit upon closing, a sixth connecting the six unit resistance in the circuit upon closing, a seventh connecting the six and one unit resistances in series in the circuit upon closing, an eighth connecting the six and two unit resistances in series in the circuit upon closing, a ninth connecting the six and three unit resistances in series in the circuit upon closing, and means for automatically opening any switches previously closed when one of the open switches is closed.

2. In a variable resistance, the combination which comprises a circuit, four resistances respectively of one, two, three and six units in value, ten switches, the first short-circuiting the circuit without the resistances when closed, the second connecting the one unit resistance in the circuit when closed, the third connecting the twounit resistance in the circuit when closed, the fourth connecting the three unit resistance in the circuit when closed, the fifth connecting the three and one unit resistances in series in the circuit when closed, the sixth connecting the three and two unit resistances in series in the circuit when closed, the seventh connecting the six unit resistance in the series when closed, the eighth connecting the six and one unit resistances in series in the circuit when closed, the ninth connecting the six and two unit resistances in series in the circuit when closed, and the tenth conmeeting the six and three unit resistances in series in the circuit when closed, and means for automatically opening any of the switches previously closed when one of the open switches is closed.

3. In a variable resistance, the combination which comprises a circuit, four resistances respectively of one, two, three and six units in value, ten switches, the first short-circuiting the circuit without the resistances when closed, the second connecting the one unit resistance in the circuit when closed, the third connecting the two unit resistance in the circuit when closed, the fourth connecting the three unit resistance in the circuit when closed, the fifth connecting the three and one unit resistances in series in the circuit when closed, the sixth connecting the three and two unit resistances in series in the circuit when closed, the seventh connecting the six unit resistance in the series when closed, the eighth connecting the six and one unit resistances in series in the circuit when closed, the ninth connecting the six and two unit resistances in series in the circuit when closed, and the tenth connecting the six and three unit resistances in series in the circuit when closed, and means for automatically opening any of the switches pre viously closed when one of the open switches is closed, the ten switches being disposed in a bank in numerical order.

4. In a variable resistance, the combination which comprises a first circuit, eight resistances respectively of one, two, three, six, ten, twenty, thirty and sixty units in value, a first set of ten switches, the first short-circuiting the first circuit without resistances when closed, the second connecting the one unit resistance in the circuit when closed, the third connecting the two unit resistance in the circuit when closed, the fourth connecting the three unit resistance in the circuit when closed, the fifth connecting the three and one unit resistances in series in the circuit when closed, the sixth connecting the three and two unit resistances in series in the circuit when closed, the seventh connecting the six unit resistance in the circuit when closed, the eighth connecting the six and one unit resistances in series in the circuit when closed, the ninth connecting the six and two unit resistances in series in the circuit when closed, and the tenth connecting the six and three unit resistances in series in the circuit when closed, means for automatically opening a previously closed switch in the first set when one of the open switches is closed, a second circuit in series with the first, a second set of ten switches with the first shortcircuiting the second circuit without resistances when closed, the second connecting the ten unit resistance in the second circuit, the third connecting the twenty unit resistance in the second circuit, the fourth connecting the thirty unit resistance in the second circuit, the fifth connecting the thirty and ten unit resistances in series in the second circuit, the sixth connecting the thirty and twenty unit resistances in series in the second circuit, the seventh connecting the sixty unit resistance in the second circuit, the eighth connecting the sixty and ten unit resistances in series in the second circuit, the ninth connecting the sixty and twenty unit resistances in series in the second circuit, and the tenth connecting the sixty and thirty unit resistances in series in the second circuit, and means for automatically opening a previously closed switch in the second set when one of the open switches in this set is closed.

5. In a variable resistance, the combination which comprises a first circuit, eight resistances respectively of one, two, three, six, ten, twenty, thirty and sixty units in value, a first set of ten switches, the first short-circuiting the first circuit without any of the resistances when closed, the second connecting the one unit resistance in the circuit when closed, the third connecting the two unit resistance in the circuit when closed, the fourth connecting the three unit resistance in the circuit when closed, the fifth connecting the three and one unit resistances in series in the circuit when closed, the sixth connecting the three and two unit resistances in series in the circuit when closed, the seventh connecting the six unit resistance in the circuit when closed, the eighth connecting the six and one unit resistances in series in the circuit when closed, the ninth connecting the six and two unit resistances in series in the circuit when closed, and the tenth connecting the six and three unit resistances in series in the circuit when closed, means for automatically opening a previously closed switch in the first set when one oi the open switches is closed, a second circuit in series with the first, a second set of ten switches with the first short-circuiting the second circuit without the second set of resistances when closed, the second connecting the ten unit resistance in the second circuit, the third connecting the twenty unit resistance in the second circuit, the fourth connecting the thirty unit resistance in the second circuit, the fifth connecting the thirty and ten. unit resistances in series in the second circuit, the sixth connecting the thirty and twenty unit resistances in series in the second circuit, the seventh connecting the sixty unit resistance in the second circuit, the eighth connecting the sixty and ten unit resistance in series in the second circuit, the ninth connecting the sixty and twenty unit resistances in series in the second circuit. and the tenth connecting the sixty and thirty unit resistances in series in the second circuit, and means for automatically opening a previously closed switch in the second set when one of the open switches in this set is closed, the switches of the first set being disposed in a bank in numerical order, and the switches of the second set being disposed in numerical order in a bank beside the first bank.

6. In a potentiometer, the combination which comprises two sets of resistances, each respectively of one, two, three and six units in value, two circuits, and a set of ten double switches, the first short-circuiting the first circuit without resistances and connecting the six and three unit resistances of the second set in series in the second circuit, the second connecting the one unit resistance of the first set in the first circuit and the six and two unit resistances of the second set in series in the second circuit, the third connecting the two unit resistance of the first set in the first circuit and the six and one unit resistances of the second set in series in the second circuit, the fourth connecting the three unit resistance oi the first set in the first circuit and the six unit resistance of the second set in the second circuit, the fifth connecting the one and three unitresistances oi the first set in series in the second circuit and the two and three-unit resistances of the second set in series in the second circuit, the sixth connecting the two and three unit resistances of the first set in series in the first circuit and the three and one unit resistances oi. the second set in series in the second circuit, the seventh connecting the six unit resistance of the first set in the first circuit and the three unit resistance oi the second set in the second circuit, the eighth connecting the six and one unit resistances of the first set in series in the first circuit and the two unit resistance oi the second set in the second circuit, the ninth connecting the six and two unit resistances of the first set in series in the first circuit and the one unit resistance of the second set in the second circuit, and the tenth connecting the six and three unit resistances of the first set in series in the first circuit and short-circuiting the second circuit, and means for automatically opening a previously closed switch of the set when any of the open switches is closed.

BURTON D. LEE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 731,209 Northrup June 16, 1903 731,210 Northrup June 16, 1903 2.234 405 Hall et al Mar. 11 1941 

